Method for producing a helical body

ABSTRACT

A method for producing a hollow, helical, electrically conducting body. The method comprising: producing a helical core made of a core material that can be at least one of liquefied and evaporated under the action of heat; coating the helical core with a first powder layer of an at least partially electrically conducting powder using a powder coating method; heating the helical core and the first powder layer to a first temperature, at which the helical core is at least one of liquefied and evaporated and at which the first powder layer is at least partially solidified in porous form, the core material exiting space surrounded by the first powder layer; and after the core material has exited the space surrounded by the first powder layer, sintering the first powder layer by heating the first powder layer to a second temperature, which is higher than the first temperature.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a 371 National Stage Application of International Application No. PCT/EP2019/059356, filed 11 Apr. 2019, which claims priority to German Application No. 10 2018 205 588.2, filed 12 Apr. 2018, both of which are herein incorporated by reference in their entireties.

TECHNICAL FIELD

The disclosure invention resides in the field of mechanical engineering, and more specifically in the field of casting technology. The disclosure relates to a method for producing a helical body, for example a coil or a spring.

BACKGROUND

A helical body shall, in particular, be understood to mean a strand-shaped body that is curved so as to take on the shape of a helix.

SUMMARY

Such helical bodies can be used as electric coils, for example, and are in particular advantageous for several purposes when the helical body itself is hollow. In this case, a current having a high current intensity can then flow through the helix, and the helix can be cooled from the inside by a liquid flowing through the cavity. However, other applications for such hollow helical bodies are also conceivable.

When such a helical body, for example in the form of a coil, is used, higher power densities can be achieved than when using solid coils, without the risk of overheating. The space utilization can thus be designed to be more efficient. However, shaping such helical hollow bodies is thus far only possible with great effort.

Moreover, a helix-shaped/helical body configured in this way also allows the skin effect, that is, the displacement of the current towards the surface of a conductor, to be reduced.

It is an object-of the present disclosure to create a method for producing a hollow helical, electrically conducting body, which can be carried out using simple means and allows such bodies to be produced cost-effectively.

Accordingly, the disclosure invention relates to a method for producing a hollow, helical, electrically conducting body. The invention furthermore relates to the corresponding helical body according to claim 13. Possible embodiments of the helical body are described in claims 14 to 17.

In embodiments, it is provided in the method that first a helical core, made of a core material that can be liquefied or evaporated under the action of heat, is produced, and thereafter is coated with a first powder layer of an at least partially electrically conducting powder using a powder coating method, and then the helical core comprising the first powder layer is heated to a first temperature, at which the core is liquefied or converted into a gaseous state, and the first powder layer is at least partially solidified in porous form, wherein the core material exits the space surrounded by the powder coating, and wherein, after the core material has exited the space surrounded by the first powder layer, the first powder layer is sintered further, in particular by heating the first powder layer to a second temperature, which is higher than the first temperature.

The method accordingly involves initially producing a helical core, for example from a foamed plastic material, and in particular from an EPS (expanded polystyrene) plastic material. This body thus produced defines the geometry of the resulting helical body. This core acting as a pattern can, as an alternative to a foam, also be produced from a wax-like, easily melting material.

The core can be connected to one or more fittings, which are treated further thereafter together with the core.

The core created in this way is then coated with an electrically conducting first powder, for example a metal powder. This coating step can be implemented in a known powder coating process. The powder that is used is a sinterable powder, which can be sintered by creating appropriate physical conditions, and in particular heating to a necessary sintering temperature. The powder layer is thereby hardened, as it adheres to the core. At the same time, the core material is melted or evaporated and is able to exit. It is particularly advantageous in the process when the powder is only sintered to such a degree that the resulting solid remains porous, so that the material of the core can at least partially exit through the pores of the sintered powder layer. All sinterable materials, and in particular sinterable metallic powders, can be used as the material for the first layer.

After the core material has exited, the powder layer can be sintered further, for example by heating to a second temperature that is elevated compared to the first temperature. Moreover, other physical parameters can also be changed, such as the pressure, so as to favor further sintering. In this way, the first powder can then be sintered to such a degree that it is sufficiently solidified, and in particular also to such a degree that the pores are closed. The temperatures can be selected in accordance with the sintering temperatures that are typical of the respective materials used.

The fittings can, if present, be coated together with the core and, in this way, become part of the helical body.

In this way, a helical body is created which essentially takes on the shape of the helical core. In embodiments, the later helical electrically conducting body has a cavity in the interior thereof, which corresponds exactly to the shape of the helical core initially situated therein. The powder layer is self-supporting, so that a stable helical electrically conducting body results from the powder layer.

The helical core, which predefines the cavity, and the powder layer can be formed in the method in such a way that the cavity forms a fluid channel in the helical body to be produced, which, for example, has one or more openings in one or more predefined locations, and in particular on at least one end of the helical body. For example, the powder layer can include a respective interruption at the one or multiple predefined locations, so that the core is exposed there. The interruption can be introduced in each case, for example, by not applying powder to the corresponding location (for example by covering the location and subsequently removing the cover), or by removing previously applied powder in a post-processing step, for example by cutting off a section of the core. However, in embodiments, it is also possible to produce the helical body with a closed cavity, and to introduce the openings after sintering in a post-processing step.

The geometry of the core can be selected such in the process that the spaces between the individual helices of the created electrically conducting body are minimized, whereby it is achieved by the helical electrically conducting body that the space is filled/utilized in an optimized manner, for example the space is filled by more than 95%.

As was already mentioned above, the sintering can be controlled in such a way that sintering of the first powder layer takes place at the first temperature, by which the first powder layer is solidified, however remains porous in such a way that the liquefiable or evaporable core material can escape through the sintered powder layer.

However, in embodiments, it is also conceivable to sinter the first powder layer in a single step or continuously, in particular when it is ensured that the material of the core is able to exit at one end of the core/of the coil to be created. This is possible, in particular, when the above-described opening, or the multiple openings, of the fluid channels is or are already defined by the powder layer applied to the helical core prior to heating, that is, when the powder layer includes the corresponding interruptions, such as at the end of the core or at the ends of the core.

In embodiments, it may be advantageous in particular for the ampacity and the creation of low electrical resistance that sintering of the first powder layer is carried out at the second temperature, by which the first powder layer is compacted so as to become impermeable to liquids, and in particular also to gases.

Moreover, in embodiments, it may be provided that the first powder layer is designed in the form of multiple consecutively applied sub-layers of the first powder. In this way, the thickness of the powder layer can be controlled well, and in particular it is also possible to consecutively apply sub-layers in this way, which can each be at least incrementally dried or partially solidified, and in particular also partially sintered, before the next layer is applied.

In embodiments, it is also conceivable to apply at least one second powder layer of a second powder to the first powder layer, in particular prior to or after a first sintering step. In this way, the sintered layer can also be suitably configured, and the resulting coil body can be provided with the necessary wire cross-section. Different powder layers can be consecutively applied in the process to implement a certain powder distribution or other desired electrical properties.

If multiple powder layers are provided, for example all powder layers can include the above-described interruptions for creating openings of the cavity. In the method, it is thus possible to provide one or more interruptions in the powder coating comprising the first powder layer and/or a second powder layer, so as to create one or more openings for the cavity defined by the helical core, which is delimited by the powder coating and then extends in the produced helical body.

In embodiments, it may be provided that the second powder is made of an electrically insulating material, and forms an insulating layer after sintering. In embodiments, the material used can be, for example, sinterable ceramic powders or other electrically insulating sinterable powders. In this case, the body, in the overall, can be produced as a functional and insulated helical body/coil body. It may be provided in the process that the second powder layer and the first powder layer are sintered simultaneously, or that the second powder layer is sintered after the first. However, another manner of solidifying the second layer, such as drying or setting, may also be selected.

During the powder coating by the first or a second or a further layer, it may be provided that the powder coating by way of the first and/or a second powder layer is carried out by spraying, dipping or using a fluidizing powder bed, or by several different consecutive aforementioned coating manners. Using the aforementioned coating manners, the entire surface of the helical body of the core can be evenly coated, even if the distance between adjoining turns of the helix is small. In this way, overall a helical body having minimal distances between the individual helices can be produced.

In embodiments, it may also be provided that the powder coating is carried out using a powder slurry and/or a powder feedstock. A powder slurry shall be understood to mean a mash-like mass that comprises a powder in a carrier liquid, including an added viscous binder. A powder feedstock shall be understood to mean a homogeneous mixture of powder and binder, which enables particularly good dimensionally accuracy during sintering.

All known sintering methods that are expedient for the respective powder used may be used as the sintering method, for example also using an appropriate gas atmosphere or inert gas atmosphere. Sinter materials that may be used include, in particular, metal powders or metal alloy powders, or mixtures of different metal powders or metal alloy powder.

In embodiments, it may be provided during the production of the core that the helical core is produced in a casting process or a foaming process, wherein the core is in particular assembled from multiple parts. In this way, it is also possible to easily produce cores in complicated shapes, for example in the shape of a helical or spiral spring. The foam can be foamed in a mold in the process, or be produced by extrusion and subsequent shaping.

It is also conceivable that the core is produced as a blank, and thereafter is brought into the shape of a helix by creating a helical recess. The blank can have a cylindrical or cube-like design, for example, wherein the blank can include a cylindrical, prismatic or cube-like cavity extending therethrough, which extends completely through the blank from a first end to the second end. The blank can thus have the design of a hollow cylinder, for example.

In embodiments, it may furthermore be provided that the helical recess is created in the core using a tool that rotates about an axis extending through the core and, at the same time, is steadily advanced along the axis. The axis of the core about which the tool rotates can extend through both the blank and the cavity in the interior thereof, so that the tool rotates at least partially inside the cavity and, at the radially outer end, extends through and removes the material of the blank. For example, the axis about which the tool rotates can be the longitudinal axis of a hollow cylinder that forms the blank. The tool can then rotate about the axis, introducing a recess into the wall of the hollow cylinder, for example by cutting, milling or sawing. The tool can be designed in the manner of a knife or a saw or a rasp, for example. The tool can also rotate about its own longitudinal axis during the processing operation, or carry out a sawing, oscillating or vibrating movement along its longitudinal axis. The tool can also be heated for melting the material of the blank.

In addition to the rotating pivoting movement, the tool can be steadily advanced parallel to the longitudinal axis of the blank, so that the tool creates a helical recess in the blank, thereby shaping the blank into an at least partially helical body.

It shall be understood that the present application also claims protection for the helical body produced in the described manner. The helical body has a cavity. As described above, the cavity is produced by way of the core, and the dimensions of the cavity are defined via the dimensions of the core.

In embodiments, the helical body includes a fluid channel having at least one openings, and preferably at least two openings, serving as the cavity. The openings can be provided at opposite ends of the helical body, for example. As an alternative or in addition, in embodiments, it is also possible to provide openings that are not located at ends of the helical body, but, for example, laterally at the windings.

The fluid channel can have a constant or a variable cross-section across the length thereof. The core can be appropriately designed for the production of the fluid channel by having a constant or variable thickness.

The helical body has outer dimensions, which can be in the centimeter to decimeter range, for example. As mentioned, the body can be cylindrical or cube-shaped, that is, have a round or rectangular base surface area, and a height extending in the direction of the cavity and the longitudinal axis. The body, however, can also be tapered in the direction of the height thereof, for example, so as to have the shape of a frustrum of a cone or of a frustrum of a pyramid, for example. The outer dimensions can, for example, be between 3 cm and 1 m in each spatial direction, that is, the base surface area can have a diameter or lateral dimensions (such as side lengths) of between 3 cm and 1 m, for example. The height can be between 3 cm and 1 m, for example.

The cross-section of the fluid channel can be polygonal or elliptical, for example, and in particular rectangular or circular. As an alternative or in addition, in embodiments, the dimensions of the cross-section of the fluid channel can be in the range of several millimeters to several centimeters, for example. A cross-sectional surface area can be between 10 mm² and 50 cm², for instance. In one example, the dimensions, for example a diameter or a side length of the cross-sectional surface area of the fluid channel, depending on which geometry it has, can be at least 5 mm and/or no more than 5 cm. A wall thickness of the material surrounding the cavity, which is made of the first powder layer or of the first and second powder layers, can be between 1 mm and 20 mm, for example.

It shall be emphasized that the features that are only described in connection with the method can also be claimed for the device, and vice versa.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be shown and described hereafter based on exemplary embodiments in figures of a drawing. In the drawings:

FIG. 1 shows a perspective view of a helical body/a coil, according to embodiments of the disclosure;

FIG. 2 shows a winding of a coil/of a helical body in a cross-sectional view, according to embodiments of the disclosure;

FIG. 3 shows a helix of a further helical body in a cross-sectional view, according to embodiments of the disclosure;

FIG. 4 shows, in a schematically enlarged form, the powder-coated surface of a helical body in a cross-sectional view, according to embodiments of the disclosure;

FIG. 5 shows a device for producing a helical core, and a core into which a recess has been partially introduced, according to embodiments of the disclosure;

FIG. 6 shows a view of a part of a helical body, comprising a power connection and/or a fluid connection, according to embodiments of the disclosure;

FIG. 8 shows a view of a part of a helical body, comprising a power connection and/or a fluid connection, according to embodiments of the disclosure;

FIG. 9 shows a view of a part of a helical body, comprising a power connection and/or a fluid connection, according to embodiments of the disclosure; and

FIG. 10 shows a view of a part of a helical body, comprising a power connection and/or a fluid connection, according to embodiments of the disclosure.

DETAILED DESCRIPTION

FIG. 1 shows a perspective illustration of an electrically conducting coil 1, serving as a helical body, which is formed by a helical, insulated, strand-shaped electrical conductor 2. The illustration of FIG. 1 shows a coil having a quadrangular, and in particular square, cross-section, wherein the conductor forming the coil itself likewise has a rectangular cross-section. The different helix layers of the conductor are rectangular and placed on top of one another at small distances.

The helical body has outer dimensions that correspond to a cuboid, having a rectangular (square) base surface area a×b, and a height h, along which the cavity extends. The body, however, can also have a different base surface area and/or be tapered in the direction of the height thereof, for example, so as to have the shape of a frustrum of a cone or of a frustrum of a pyramid, for example. The outer dimensions a, b and h are between 3 cm and 1 m in each case.

FIG. 2, by way of example, shows the cross-section of an insulated conductor, which can be used, for example, to produce a coil, as it is shown in FIG. 1. In FIG. 2, the hollow outer portion formed of a sintered powder is denoted by reference numeral 3, and the core 4 is shown within the powder coating 3, which is made of a foam material, and in particular EPS, for example. The configuration shown in FIG. 2 results, for example, directly after the helical body 4 has been coated with a first powder 3. The powder 3 is designed to be at least partially electrically conducting, and is made of an electrically conducting material, for example a metal or a metal alloy. It can also be made of a mixture of two or more powders, which are preferably all electrically conducting.

In the shown configuration, the coated core 4 can be heated to a temperature below the melting temperature of the first powder, wherein the material of the core 4 either evaporates or liquefies. The material of the core can then escape at one end of the layer/coating, or through the coating itself, so that only the coating remains, which is sintered at the same time and thereby solidified. The sintering process is usually controlled in such a way that, in a first phase of the sintering process, when the first powder layer 3 is still permeable to gas or fluid, the core is liquefied or rendered gaseous and thereby, for example, is also able to exit through the coating 3/powder layer 3.

After the material of the core 4 has exited, the sintering process can be continued, either by maintaining the temperature at a stable level for an additional period of time, or by slightly raising the temperature, so that the sintering process progresses further. This can be continued until the first powder layer has been densified, thereby having become impermeable to gas/fluid. The sintering process can be carried out in an inert gas atmosphere, for example.

The cavity defined by the core 4 then forms a fluid channel, which emerges at the opposite ends of the coil in the example. A cross-sectional surface area p×q of the fluid channel, which is rectangular in the present example, is between 10 mm² and 50 cm², for example. Side lengths p and q of the cross-sectional surface area of the channel can be several millimeters to several centimeters in examples, corresponding to the cross-sectional surface area. A wall thickness w of the material surrounding the cavity, which comprises the first powder layer, can be between 1 mm and 20 mm, for example.

As an alternative or in addition, in embodiments, it is also possible to provide openings of the fluid channel that are not located at ends of the helical body, but, for example, laterally at the windings. The fluid channel can have a constant or a variable cross-section across the length thereof.

FIG. 3 shows a configuration including a core 4′ having a round cross-section, which is surrounded by a first powder layer 3′ and an outer second powder layer 5. The first powder layer 3′ is composed of an electrically conducting powder, for example a metal powder, while the second powder layer 5, which surrounds the first powder layer 3′, is made of or produced from an electrically insulating material, such as a sinterable ceramic powder or any other sinterable electrically insulating powder.

During the joint sintering of the first and second powder layers, two hard self-supporting layers are created, wherein the inner layer 3′ is electrically conducting and forms the conductor of the helical body, and the outer layer 5 forms an outer insulation for the conductor 3′. The powder layers 3′ and 5 can also be applied and sintered consecutively. Since powder coating by way of conventional powder coating processes, such as dipping or spraying, requires very little space, it is also possible for windings of the coil that are located very close together, as shown in FIG. 1, to be evenly coated with a powder layer, which is then solidified by way of sintering. As a result, a helical electrically conducting body having little space requirement and little clearance between the individual windings, and optionally also including an insulation, can be easily produced. A coil or a spring can be produced using such a helical body, with optimal space utilization.

A cross-sectional surface area of the core 4 or fluid channel, which is round in the present case, has the radius r, which is between 5 mm and 5 cm, for example. As an alternative or in addition, the surface area can be between 10 mm² and 50 cm², for example. A wall thickness w′ of the material surrounding the cavity, which comprises the first and second powder layers, can be between 1 mm and 20 mm, for example.

FIG. 4, in an enlarged schematic illustration, shows a first powder layer 3 and a core 4, wherein individual grains of the powder layer are distinguishable. The material of the core is evaporated or liquefied, and can pass through the pores of the first powder layer 3 according to the arrows 6, 7, as long as the material of the first powder layer has not yet been sintered to a fluid-tight state.

FIG. 5 shows a hollow cylinder 8, which serves as a blank for producing the core. This blank 8 can be made of a foam material, for example, but can also be made of a wax or a similarly meltable material. The cylinder 8 has a cylindrical cavity 9 so as to be designed in the overall as a hollow cylinder having a hollow cylinder wall 10. The longitudinal axis of the hollow cylinder is denoted by reference numeral 11.

A device for introducing a helical recess into the hollow cylinder 8 is shown beneath the hollow cylinder 8, which comprises a vertically arranged shaft 12 that is mounted rotatably about the longitudinal axis thereof on a holder 17. A tool 13 is arranged on the shaft 12, which projects perpendicularly from the shaft 12. The tool 13 is connected to the shaft 12 by means of a vibratory or saw drive 14. This drive 14 can effectuate an oscillating movement of the tool 13 in the direction of the double arrow 15. Instead of a vibratory drive 14, it is also possible for a heater for the tool 13 to be provided.

When the shaft 12 is driven rotatably, the tool 13 moves on a circular track about the axis 11, dividing the hollow cylinder 8 when the tool creates a path for itself through the cylinder wall 10. This may take place, for example, by a rasping or sawing motion, provided the tool 13 includes teeth. It is also possible for a heater of the tool 13 to be provided, for heating the tool so as to melt the material of the hollow cylinder 8. Simultaneously with the rotational movement about the axis 11, an axial advancement of the tool 13 in the direction of the axis 11 is provided, which takes place, for example, at a constant speed. The advancement speed, however, can also be changed to create different sections having different pitches. By combining the rotational and advancement movement of the tool 13, a helical recess 16 is introduced into the hollow cylinder 8. The portion of the hollow cylinder 8 that remains between the individual turns of the continuous recess 16 likewise has the shape of a helix. This body can be used as the core for the helical body to be produced, and can later be covered with a first powder layer. After the first powder layer has been sintered and the core material removed, a hollow, helical electrically conducting body in the shape of a coil arises.

FIG. 6 shows an end section of a hollow helical body 1 in a perspective representation. The helical body can have the shape of a spiral, having a diameter that decreases or increases from winding to winding of the helix, but may also have the shape of a screw having a constant diameter. At one end or both ends, the helical body 1 comprises a fitting 20, which takes on the shape of a sleeve, and in particular a cylindrical sleeve. The sleeve 20 can be made of a metal, for example iron, steel, stainless steel, copper or brass. The sleeve 20 can also include a metallic connecting lug 21 for establishing an electrically conducting connection.

FIG. 7 shows that, in the case of the production method, the core 4 is connected to the fitting 20, and thereafter both are jointly coated with a powder layer 3, 3′. This is indicated by the arrows 22.

FIG. 8 shows that, when the core 4 is connected to the device 20, the core 4 can end at the device, and this may be attached to the core.

FIG. 9 shows that the core 4 can also extend into a through-opening 20 a of the device. For this purpose, the core 4 can be cast onto and into the device 20 during the production thereof.

FIGS. 8 and 9 show that the coating 23 is applied both to the core 4 and to the sleeve 20, so that the sleeve 20, without further measures, is connected to the portions of the helical body 1 that are formed by the coating 23, after the core has been removed. Such a connection can be provided at both ends of the body 1.

In addition to an electrical connection, the sleeve(s) 20 can also form a fitting for the connection of a fluid line for cooling. For this purpose, the sleeve can also include a screw thread 24 (see FIG. 10) and/or a bayonet catch and/or a seal and/or a sealing seat.

Using the disclosure, a hollow helical body having a low space requirement and high space utilization can be created, which can be used very efficiently as an electric coil due to the option of internal cooling. 

1.-17. (canceled)
 18. A method for producing a hollow, helical, electrically conducting body, the method comprising: producing a helical core made of a core material that can be at least one of liquefied and evaporated under the action of heat; coating the helical core with a first powder layer of an at least partially electrically conducting powder using a powder coating method; heating the helical core and the first powder layer to a first temperature, at which the helical core is at least one of liquefied and converted into a gaseous state and at which the first powder layer is at least partially solidified in porous form, the core material exiting space surrounded by the first powder layer; and after the core material has exited the space surrounded by the first powder layer, sintering the first powder layer by heating the first powder layer to a second temperature, which is higher than the first temperature.
 19. The method of claim 18, wherein after heating the helical core and the first powder layer to the first temperature, the first powder layer is solidified and remains porous, such that the core material that is at least one of liquefied and evaporated escapes through the solidified first powder layer.
 20. The method of claim 18, wherein after the sintering of the first powder layer at the second temperature, the first powder layer is compacted to become impermeable to liquids and gases.
 21. The method of claim 18, wherein the first powder layer is formed in the form of multiple consecutively applied sub-layers of the powder.
 22. The method of claim 18, comprising at least one second powder layer of a second powder applied to the first powder layer, prior to or after heating the helical core and the first powder layer to the first temperature.
 23. The method of claim 22, wherein the second powder is made of an electrically insulating material and forms an insulating layer after one or more of heating at the first temperature and heating at the second temperature.
 24. The method of claim 18, wherein the powder coating method includes one or more of spraying, dipping and using a fluidizing powder bed.
 25. The method of claim 18, wherein the powder coating method includes one or more of a powder slurry and a powder feedstock.
 26. The method of claim 18, wherein the helical core is produced in one or more of a casting process and a foaming process, such that the helical core is assembled from multiple parts.
 27. The method of claim 26, wherein the helical core is produced as a blank, and thereafter is brought into the shape of a helix by creating a helical recess.
 28. The method of claim 27, wherein the helical recess is created in the helical core using a tool that rotates about an axis extending through the helical core and, at the same time, is steadily advanced along the axis.
 29. The method of claim 18, comprising at least one interruption in powder coating of the first powder layer or a second powder layer to create an opening for a cavity defined by the helical core, the cavity being delimited by the powder coating.
 30. A helical body, comprising a cavity and being produced by the method of claim
 18. 31. The helical body of claim 30, wherein the cavity is designed as a fluid channel and includes at least one opening.
 32. The helical body of claim 30, wherein outer dimensions of the helical body are between 3 cm and 1 m in each spatial direction.
 33. The helical body of claim 30, wherein a wall thickness of a material surrounding the cavity is between 1 mm and 20 mm.
 34. The helical body of claim 30, wherein a cross-section of the cavity designed as a fluid channel is one of polygonal and elliptical and has a cross-sectional surface area of between 10 mm² and 50 cm². 